Method for cutting gramophone records, and articles produced thereby

ABSTRACT

A method for cutting a modulated groove into the surface of a gramophone record disc. The groove is cut by a cutting stylus the tip of which is guided relative to a constant depth cutting plane located well below the lowest point of wobble and/or irregularity of the original disc surface. Thus, the parts of the groove crest formed when walls of adjacent grooves intersect during cutting of the disc are substantially below said lowest point of the original disc surface.

United States Patent [191 Rabe [ Nov. 26, 1974 METHOD FOR CUTTING GRAMOPHONE RECORDS, AND ARTICLES PRODUCED THEREBY Inventor: Erich Rabe, Nurnberg, Germany Assignee: Polyband Gesellschaft Fur Tontrager mbl-I & Co. KG, Munich, Germany Filed: Aug. 10, 1971 Appl. N0.: 170,606

Related U.S. Application Data Continuation of Ser. No. 811,121, March 27, 1969, abandoned.

Foreign Application Priority Data Mar. 27, 1968 Germany 1772070 us. Cl. 274/42 R, 274/13 R, 274/46 R int. Cl. ..Gl1b 3/72 Field of Search 274/46, 42, 13

Bswurf Hswarf 3 y 6 5 [56] References Cited UNITED STATES PATENTS 2,864,896 12/1958 Boontje et al. l79/l00.4 3,528,665 9/1970 Redlich 274/46 Primary Examiner-Louis R. Prince Assistant Examiner-Charles E. Phillips Attorney, Agent, or FirmMaky, Renner & Jeffrey [57] ABSTRACT A method for cutting a modulated groove into the surface of a gramophone record disc. The groove is cut by a cutting stylus the tip of which is guided relative to a constant depth cutting plane located well below the lowest point of wobble and/or irregularity of the original disc surface. Thus, the parts of the groove crest formed when walls of adjacent grooves intersect during cutting of the disc are substantially below said lowest point of the original disc surface.

10 Claims, 9 Drawing Figures METHOD FOR CUTTING GRAMOPHONE RECORDS, AND ARTICLES PRODUCED THEREBY The present application is a continuation of application Ser. No. 811,121, filed Mar. 27, 1969, now abandoned.

BACKGROUND OF THE INVENTION When gramophone records are produced, grooves are cut in the surface thereof by means of a cutting stylus, which grooves must be at a distance from each other such that when the cutting stylus is deflected to form the maximum extent, the grooves do not come so close together that when the record is played by means of the pick-up needle, it jumps into the adjacent groove.

A certain minimum safety distance must be left between the grooves to prevent the pick-up needle jumping from one groove to the next, so that when the record is cut a part of the flat disc surface remains. The groove depth and the radius of the pick-up needle are so related that the point of contact between the groove surface and the conical tip of the pick-up needle is approximately 0.7 times the radius of the pick-up needletip above the theoretical groove bottom. Accordingly, if there is any overlap of two adjacent groove walls such as to form a crest, the minimum height of this groove crest must be 0.7 times the value of the radius of the conical needle-tip, although a safety distance of from to percent of the height of the groove crest above the theoretical point of contact will be included.

It is also known in the production of records, to impress into the disc surface grooves of varying crosssectional shape, for example, there is known a V- shaped cross-section with equilateral or right-angled formation, and rounded groove faces, squared groove faces, rectangular grooves, arcuate grooves, sawtoothlike grooves, flat-arc grooves, reference being made to US. Pat. Nos. 1,580,567; 1,246,651; French Pat. Nos. 421,491; 563,069; 959,275; 1,072,259, and German Pat. Nos. 757,878; 624,299; 547,712; 896,123 and 225,036. It is also known to provide additional guide grooves, in particular guide shoulders, in the region of the groove containing the recording proper, in order to prevent the above-mentioned jumping of the pick-up needle.

However, other attempts have also been made to apply as much recording content as possible to the record. Thus, in a known method, the groove which has already been cut was sensed. The deflection of this groove controls the distance between the groove which has already been cut and the adjacent groove which has still to be cut, thus avoiding overcutting of the grooves and, consequently, jumping of the pick-up needle.

The present invention is concerned with the problem of providing a method for applying a recording to a master plate which suffers from irregularities and wobble, both in lateral track, hill-and-dale track and in twocomponent track, which method permits as large a recording content as possible to be applied to a given disc surface, while eliminating any jumping of the needle when the record is played using a conventional pick-up needle, when the largest amplitudes of adjacent grooves coincide. In accordance with the present invention, each particular part of a groove can be safely cut even when there occur disc wobble and disc irregularity, without the necessity for a surfacing operation which was previously necessary to deal with disc irregularity. The present invention also concerns the disc resulting from the aforesaid method.

SUMMARY OF THE INVENTION According to the present invention there is provided a method of cutting a groove into the surface of a gramophone record disc using a cutting stylus which is deflected at the required frequency modulation frequency and which cuts out a part of the material which is of a shape corresponding to the section of the cutting stylus, wherein the cutting stylus is guided with its tip at a depth of cutting plane with respect to the lowest point of wobble and irregularity of the original disc sur face such that the parts of the groove crest which is formed when walls of adjacent grooves intersect are located substantially below said lowest point of the original disc surface. The crests and bottoms of said grooves when said grooves are unmodulated are in flat planes parallel to and in, respectively, the cutting plane of the grooves. Modulation of the grooves varies the depth of. the grooves from the cutting plane only by amounts equal to the modulation signal. 1

In accordance with the invention, a conventional master plate can be used which can therefore suffer from considerable irregularities and a considerable wobble, without the need for particular precautions or preliminary re-working, and without the support surface of the turntable and the turntable bearing having to be produced and used with excessive precision, even when used over a prolonged period, with the resulting wear and tear. v

Because the highest groove wall crest formed in the cutting operation is kept substantially below the lowest point of wobble or irregularity, the variations due to the wobble in the amount of disc material cut out are only slight with respect to the average amount of material removed. This substantially eliminates slight variations in the cutting turning moment to be applied and thus crackling noises arising out of the fluctuating cutting force. Furthermore, the elastic deformations of the cutting apparatus which occur because of the varying cutting pressure are small and do not appear as audible frequencies. 0

A substantial advantage which is achieved at the same time is that the swarf which is cut out of a certain minimum thickness and can therefore be sucked off as it is formed, without their being any possibility of the swarf breaking. Because of the surfacing operation which is carried out according to the invention with the cutting operation, this minimum swarf thickness is considerably thicker than the triangular swarf which is produced with conventional means and which only corresponds to the cross-section of the groove. A further advantage results from the-fact that with a certain amplitude maximum being observed, when the pick-up needle-tip is of a given radius and when maximum converging adjacent groove amplitudes coincide, the groove crest is still at a sufficient safety distance above the parof the cutting face of the cutting stylus is extended in the plane of the leading groove wall upwardly to at least above the level of the highest point of wobble or the highest point of irregularity of the disc surface. Thus, when the groove is cut, a substantially trapezoidal swarf cross-section and thus a stable strip of swarf is produced, and a cutting stylus with straight cutting edges which is easy to produce can be used, while regrinding of the cutting stylus is easy. In addition, the swarf which is to be removed is produced in a predetermined and easily maintainable rolled-up form. These advantages are found with hill-and-dale recording, lateral recording and two-component recording.

Another substantial advantage is that the cutting burr formed is only single-sided and not, as previously, double-sided, and moreover because the effective pick-up point is at a given distance from the minimum height of groove wall, the cutting burr cannot result in the production of troublesome noise.

An important difference between the conventional cutting method and the cutting method according to the invention is that with the known methods, when the amplitudes of adjacent grooves converge, it must be possible for a sharp crest to be formed if necessary on the disc surface with the given groove depth or groove wall height being fully maintained, whereas with the method according to the invention it is possible for the two groove walls to intersect, reducing the dimension of the groove wall or groove crest height to a value such that the effective pick-up point is only for example about a percent safety distance below the groove crest height, so that with a conventional pick-up needle-tip radius of, for example, 17 u, the groove crest can sink to a height of, for example, 12 ,u, measured from the theoretical sharp-angled groove bottom.

Diverging maximum amplitudes in adjacent grooves do not form, as in conventional methods, a wide flat disc surface, the width of which also depends on the disc wobble and disc irregularity, but in this case too there is formed a sharp groove wall intersection crest which is only raised in height with respect to the mean cutting plane determined by zero amplitude.

A further feature of the method according to the invention provides, for the production of records with perpendicular reproduction, that only one groove wall, which is inclined for example at 45 to the disc surface, is modulated, the other groove wall being cut without modulation and being substantially perpendicular to the disc surface. The result of this is that the space required for the second wall and the space required for the modulation of that wall can be saved so that it is possible for the grooves to be brought even closer together and for the recording content of the record to be further increased. This method forms a substantially sawtooth-like groove cross-section. Although substantially sawtooth-like groove crosssection are known in the prior art, these were primarily for the purpose of improving pick-up needle guidance and thus enablingthe pick-up needle to slide in the groove more easily, without any specific intention of increasing the recording content. On the contrary, the inclined position of the pick-up needle resulted in prior art arrangements in a reduction of the recording content due to an increase in the groove distance (German Pat. No. 225,036);

According to another aspect of the method accord ing to the invention, in the region of the run-in groove the groove bottom is cut to a depth corresponding to the following mean cutting plane and both the groove walls are cut in a straight line extending to the original disc surface, with a space being maintained between adjacent run-in groove walls. This provides that in the region of the run-in groove, without changing the setting of the cutting head, the groove depth mewsured from the original disc surface is a multiple of the depth of the conventional run-in groove, resulting in an assured run-in, without the possibility of the pick-up needle jumping out of the groove even when the contact pressure is extremely light.

The same advantages may also be achieved in accordance with the present invention in the formation of the indication groove. In the region of an unmodulated indication groove which is to be formed between two modulated grooves, the cutting stylus continues with its tip at the depth of the preceding mean cutting plane and is advanced with a groove spacing such that both groove walls when cut extend to the level of the original disc surface and adjacent groove walls have a space between them.

Another feature of the method according to the invention provides that in the region of the run-out groove the groove bottom is cut at a depth corresponding to the preceding mean cutting depth and both the groove walls are cut to extend in a straight line upwardly to the original disc surface, with a space being maintained between adjacent run-out groove walls. Thus, without changing the setting of the cutting head, the fact that the cutting stylus moves on into the original disc surface which was substantially higher than the preceding cutting plane or groove crest height results in a depth of run-out groove such that the considerable switch-off forces which are to be applied by the movement of the pick-up arm can assuredly be applied and there is no possibility of the pick-up needle jumping over a groove or snagging in a self-cut groove.

An advantage of the above-specified method steps lies in the fact that by forming the mean cutting plane substantially below the original disc surface and by thus making the modulation groove crest which is formed in the cutting operation also lie substantially below the original disc surface, the modulation groove region is not damaged even when records are placed on top of each other without protection sleeves, even when there is fine dust or the like on the surface of the record.

As a result, there is no necessity to provide the record with a reinforced rim, as is described for example in U.S. Pat. No. 3,042,413. Likewise, there is no necessity to provide an inner region of increased thickness, thus resulting in a substantial simplification and reduction in cost of the production of the master plate and at the same time substantially reducing the danger of damage to the modulation grooves of the finished records. Using this method of the invention a record can be produced which has both a rim region which is raised above the modulation groove region and an inner region inward of the run-out groove which is higher than the former region.

A further objective of the present invention resides in producing a disc or record having the above described characteristics, that is, wherein the groove crests always lie at a predetermined safe distance below the lowest point of irregularity of the original disc surface, and wherein the crests and bottoms are located in planes spaced from the cutting planes only by amounts equal to the modulation signal.

In order to carry out the method according to the invention, it is necessary for the cutting apparatus to be of suitable construction. In a known cutting apparatus the cutting head is carried by a arm which can be moved over the record surface to be cut by means of 5 a guide sleeve running on a guide shaft which can also be in the form of a threaded spindle. Fixed on the side of the guide shaft which lies opposite the cutting head is a further arm on which a counter-weight is adjustably mounted. This counter-weight serves to compensate a part of the weight of the cutting head so that by moving the counter-weight the effective pressure of the cutting stylus of the disc surface can be adjusted within certain limits.

In this case it is assumed that the disc material distributed over the whole of the disc face results in a uniform cutting force and therefore also a uniform depth of cut. In practice, however, the material of which the disc is made is not of equal resistance at every point of the disc surface so that for these reasons alone the cutting force and consequently the depth of penetration of the cutting stylus varies, because of the variations in the resistance of the material. In addition, it is not possible to maintain a degree of disc irregularity which is slight with respect to the groove depth and it is equally impossible to keep the degree of turntable wobble substantially less than the groove depth. Furthermore, the setting angle of the cutting faces of the cutting stylus varies because of the groove radius decreasing in size toward the middle of the disc.

Taken overall, the above factors which influence groove depth can be statistically added as well as subtracted. If it is assumed that in order to apply as much recording content as possible to the disc, the groove depth is made as small as possible, the above mentioned factors can easily result in breaks in the grooves.

The cutting apparatus is therefore so constructed that in spite of these factors, the cutting operation is performed in accordance with the method of the present invention. The cutting apparatus comprises a cutting head which is transversely displaceable over the disc surface by means of an advancing device and a guide means. The cutting head is positively guided on a guide plane formed parallel to the disc surface. In comparison with the conventional cutting apparatus, this results in a defined cutting plane which is not varied in its relative position with respect to an ideal disc surface, in dependence on disc material resistance, irregularity, disc wobble, bearing wear, and cutting pressure in the individual regions of the disc.

The carriage carrying the cutting head is guided in a predetermined cutting plane by at least two guide shafts, guide ribs or the like which are arranged parallel and at a spacing. This forms a defined plane, defined herein as the cutting plane, which has one alignment, substantially parallel to the turntable surface, and which therefore eliminates detrimental influences on the plane of movement of the cutting head. This ensures that the minimum groove spacing can be achieved, depending on the cutting stylus or pick-up,

needle shape which is selected or standardised, resulting in the maximum recording content without needle jumping. The location of the groove bottoms and crests are therefore always in planes parallel to the cutting plane, with the location of the groove crests and bottoms varying from such cutting plane only by amounts equal to the modulation signal.

It is desirable for the cutting head advancing spindle to engage the guide carriage between the guide shafts, guide ribs or the like. This eliminates any tipping movement which results from the friction of the carriage guide means and which causes detrimental and undesired elastic deformation. With this arrangement it is of particular advantage if the means guide plane lies substantially in the cutting plane so that the difference in height between the planes of application of force is eliminated; as such a difference results in a tilting movement and thus a fluctuation in cutting depth. Two adjacent parallel guide shafts can be provided to guide its carriage in a straight line, while a further guide shaft with a guide plane parallel to the cutting plane is arranged parallel to the said two guide shafts on the side opposite the cutting head.

Thus, parts which are easy to manufacture can be used to provide a guide plane with a broad base, which does not suffer any deformation under the influence of external or internal forces so that it is easy for the groove depth to be maintained constant within the defined tolerances.

It is also advantageous for the cutting head and/or the arm on which it is mounted to be adjustable for height with respect to the cutting plane. With this arrangement, it is easy'for the desired depth of cut and thereby the cross-section of the swarf cut out, to be established so that the cutting plane lies substantially below the lowest point of wobble and/or irregularity and at the same time a swarf is produced which is stable and which does not break up.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in greater detail by way of example hereinafter with reference to embodiments. In the drawings:

FIG. I shows a diagrammatic section through a master plate, showing the cutting operation,

FIG. 2 shows a diagrammatic cross-section of the groove formation with conventional lateral track,

FIG. 2a shows a plan view of the groove formation of FIG. 2,

FIG. 3 shows a diagrammatic view of the groove for- DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. I, a recording material I, for example in the form of a layer of lacquer, is applied on all sides to a carrier disc 2 which may be made for example of aluminium. The layer thickness S of the layer of recording material I can vary locally, both to form an increase +AS in the thickness of material I and also to form a decrease AS in thickness of material 1. These local variations :L-AS can be statistically distributed over the whole of the disc surface, although it is desirable for these variations to be kept within close tolerances.

With a conventional standardised groove depth RT of, for example, 27 u, a variation in layer thickness of, for example, 20;; can result in the depth of the groove being less than the minimum groove depth permissible, so that such a disc cannot be used to produce a matrix.

Added to this is the fact that the thickness S of the layer of recording material 1 can vary by a given amount with respect to the surface of the opposite layer so that when the disc is rotated, there is a periodic wobble Schl and Schl to which is added the wobble in the turntable, whereby in the most unfavourable condition, all the above errors result in an excessively large or an excessively small groove depth.

Because the cutting stylus is guided with its tip at the cutting plane SchE which is substantially below the lowest point of the disc surface 11, when the disc 2 is cut there is a mean material removal MA, which creates an ideal cutting plane with respect to the theoretical groove bottom 6 or groove crest 7, while at the same time the leading cutting edge 9 of the cutting stylus cuts out a swarf of recording material 1 of a depth Hswarf such that together with the swarf width Bswarf resulting from the groove spacing RA, it forms a swarf 3 which is sufficiently strong so that it cannot break off during the cut and can be safely sucked away or removed in conventional manner. The relatively large distance between the cutting plane 10 and the original mean disc surface 11 results at any event in the adjacent groove walls 4 and 5 being fully cut out so that a sharp groove crest 7 is formed over the entire length of the groove by the intersection of the groove walls 4 and Depending on whether lateral track, hill-and-dale track or two-component track is used, the groove crest 7, and in the last two types of tracks,the groove bottom 6 as well, are in the form of a space curve. This results in the complete elimination of the variations iAS in layer thickness and of the disc wobble Schl i, so that with a minimum groove spacing RA (FIG. 2), there is no fear that when there is a maximum modulation amplitude, the distance between groove bottom 6 and groove crest 7 will fall below a predetermined minimum. As a result it is possible considerably to increase the recording content in comparison with a conventional record. A run-in groove 8 can also be provided in conventional manner.

By way of illustration, FIG. 2 shows that with a conventional record a groove spacing RA of, for example, 125p. is maintained when the amplitude is nil. When there are converging amplitudes A A in adjacent grooves, the deflection of the two grooves can then result in the formation of a sharp crest.

With a groove depth RT of, for example, 3011. and a pick-up needle radius of 17 1,, for example, the effective pick-up point AT is 12p. above the theoretical groove bottom so that the theoretical distance from the disc surface of 18a is used. However, as the above discussed wobble and variations in layer thickness must be taken into account, and they can often add up to, for example, 18 1,, substantial parts of the possible groove space cannot be used for reasons of safety. As illustrated in FIGS. 2 and 2a, the spacings between the groove top As shown in FIG. 3, when the method according to the invention is used with pure lateral track, on the assumption that with the tip radius R of the pick-up needle being, for example, l7p., the pick-up point AT is 12p. above the theoretical groove bottom 6 or the cutting plane SchE, and on the assumption that there is a safety distance SA of 1/.L over the minimum groove depth RT the minimum groove depth RT is 13p.

when the amplitudes of adjacent grooves converge.

With a maximum lateral amplitude of 1, for example, the mean groove spacing is 34a, which provides an increase in recording content of approximately 3% v times.

FIG. 3 also shows the various possible groove crosssections when lateral track is used, depending on the direction of the maximum amplitude A A while it is apparent that both the height of the groove crest 7 and its relative position in space can vary, as can be seen from the curve of the geometric location for the groove crest 7 COR The geometric location for the groove bottom is in this case a straight line GOR which lies in the cutting plane SchE symmetrically to the groove bottom 6.

FIG. 4 shows on an enlarged scale and in diagrammatic form the possible positions of the groove walls and groove crests when two-component track and hilland-dale track is used. In this case there is assumed a mean unmodulated groove RU, while there is superimposed on the shape thereof a negative or a positive modulation amplitude A and A respectively.

In an imaginary example, the means groove spacing RA achieved may be 331., for example, on which may be superimposed a positive or a negative amplitude of 3p. so that a minimum groove spacing of 27p. and a maximum groove spacing of 39p. can be achieved. In this case, depending on the particular modulation amplitude, the geometric location of the pick-up needle-tip can move within a square formed by the points 0 02, 03, 0

When pure hill-and-dale track is used, the movement of the geometric location is limited to a perpendicular straight line between 0 and 0. When hill-and-dale track is used however, with the assumed restriction in groove width being maintained, converging modulation amplitudes totalling 8;, for example, can be accommodated, or with the total restricted to 6a, the recording content can be further increased by 25 percent.

FIG. 5 shows another groove formation which permits further increase in recording content over the above described groove formations. For this purpose the recording is only applied to one groove wall and the other groove wall is unmodulated and substantially perpendicular, resulting in a sawtooth-like cross-section.

In FIG. 5, RU means the unmodulated groove which can be set at an angle of 45 with respect to the disc surface. The modulation is applied to this wall with an amplitude of from A +to A The steep sawtooth wall SF is unmodulated and only acts as a smooth guide face,

angle of the sawtooth groove wall, or the axis of the cutting head can be aligned in the direction of the axis of the sawtooth groove wall, one cutting edge of the cutting stylus lying parallel to the axis of the cutting head.

FIG. 6 shows a diagrammatic cross-section taken through a fully cut master disc formed in accordance with the invention, in which a carrier disc 2 is coated on both sides with recording material 1. A run-in groove 8 with a greater pitch than the conventional modulation groove pitch, is cut in the outer rim region in a run-in groove region ERB such that the groove bottom 6 lies at the level of the mean cutting plane 10 of the modulation grooves which are distributed over the modulation groove region MB With this arrangement, the position in respect of height of the original disc surface 11 above the cutting plane 10 results in a run-in groove which is extremely deep and broad at its upper edge so that it is considerably easier to insert the pickup needle.

If it is necessary to provide an indication groove, cutting is continued without modulation in the method according to the invention, just with a momentary increase in the groove pitch without adjusting the depth of the cutting head, whereby an indication groove is cut in an indication groove region KRB, while the bottom 6 of the indication groove again lies in the mean cutting plane 10 of the preceding modulation groove region MB, so that here too there is cut an indication groove which has groove walls extending up to the original disc surface 11, so that when the pick-up needle is put into the indication groove instead of into the run-in groove, the operation can be carried out easily and without mistake.

Cutting can then be continued according to the method of the invention in the same cutting plane 10 in the modulation groove region MB as far as the runout groove region ARB, wherein the groove bottom 6 again lies at the level of the preceding cutting plane 10 of the modulation groove region MB,, or MB Here too however the groove walls extend up to the level of the original disc surface 11, forming a run-out groove which is very deep and very wide at its upper edge and which transmits the switch-off forces from the pick-up needle to the pick-up ann without the pick-up needle jumping out of the run-out groove or being able to cut its own groove.

FIG. 7 shows an apparatus for producing the above described groove formations, the essential feature of I which is that the cutting head 101 is positively guided parallel to the cutting plane, irrespective of the variations in the disc surface.

For this purpose the cutting head 101 is guided adjustably by means of a fixing screw 103, which is carried by a guide sleeve 102 on a mounting arm 106. The modulation signal is supplied via leads 104. The cutting stylus 105 is guided over the surface of the master disc 111 which lies on a turntable 112 carried by the tumtable shaft 113. The turntable shaft 113 is mounted with as little wobble and play as possible in a bearing 114 which is mounted on a base plate 115 which carries at a distance two guide lugs 116, between which two guide shafts 118 and are fixed parallel to each other and parallel to the plane of rotation of the tumtable 112.

Attached to each of the guide lugs 116 is a guide shaft support arm 124 in which is mounted an outer guide shaft 109 arranged parallel to and at a spacing from the guide shafts 118, 120. A guide carriage 117 is mounted substantially without play on the inner guide shafts 118 and 120, and can be moved along the guide shafts 118 and 120 by means of an advancing spindle 119 which is in suitable drive communication with the turntable shaft 113.

At its inner end the guide carriage 117 carries a forkshaped mounting lug 121 in which a pivot head 123 is mountedwithout play but is rotatable, by means of a mounting pin 122. The pivot head 123 carries the inner end of the mounting arm 106. The outer end 107 of the mounting arm 106 carries a depth-of-cut adjusting screw 108 which can slide on the surface of the outer guide shaft 109. The outer guide shaft 109 can have an improved guiding action by being provided with a guide face 1 10 which is arranged parallel to the cutting plane and parallel to the guide shafts 118, 120. In this case the weight and strength of the whole assembly is so great that even when there is an extremely large swarf removal, there is no possibility of elastic deformation or lifting of the cutting head 101 from the disc surface. Consequently, the above described apparatus can provide an ideally flat surface in respect of the mean groove depth, irrespective of the disc thickness and the disc wobble. The depth of cut of the cutting head 101 may be easily adjusted by means of the adjusting screw 108.

Another suitable apparatus is illustrated in FIG. 8, in which a master disc 111 lies on a turntable 112 which is carried by a turntable shaft 113 mounted in a bearing 114. The turntable bearing 114 is connected to a base plate 115, on which double-prism guide ribs 128 and 129 or the like are arranged in a plane parallel to the plane of the turntable 112.

A guide carriage 117 which is provided with guide grooves corresponding to the guide ribs 128 and 129 lies on the guide ribs 128 and 129. The guide carriage 1 17 can be displaced parallel to the plane of the tumtable 112 by means of an advance spindle 119 which is in drive communication with the turntable axis 113.

The guide carriage 117 carries a mounting arm 106,

at the end of which is mounted a depth adjustment support which may be adjustable for angle. Arranged on this depth adjustment support 125 is a correspond ing carriage which is adjustable by means of a depth-ofcut adjustment screw 108. It is possible in either form of apparatus for the support or the cutting head 101 to be set at an angle with respect to the turntable shaft 113 in order to produce the above described sawtooth groove.

In both forms of apparatus, it will be noted that the cutting plane is thus located at a predetermined, adjustable level above the vertically fixed turntable thereby eliminating the effect of surface irregularities. The groove bottoms and crests are located at predetermined depth above, at, or below the cutting plane, and thus the turntable, depending on the modulation signal.

Various further modifications may of course be made without departing from the scope of the invention as defined by the appended claims.

There follows, for ease of reference, a list of the various symbols and abbreviations used in the specification and drawings:

S Layer thickness Variation in layer thickness MA Material removed RT Mean groove depth MR Material remaining RA Groove spacing Schl Wobble in the direction of an increase in layer thickness Schl Wobbel in the direction of a decrease in layer thickness B Swarf width H Swarf depth SchE Cutting plane RU Unmodulated groove S max Maximum layer thickness S min Minimum layer thickness A max Maximum amplitude in the direction of the disc axis A max Maximum amplitude in the direction of the disc rim RT min Minimum groove depth RT Mean groove depth Ar+ Groove crest displacement in the direction of the disc axis Ar Groove crest displacement in the direction of the disc rim COR Enveloping geometric locations of the groove crest GO ball m Geometric location of the groove bottom RO Mean space remaining between grooves Minimum space remaining between grooves RO Maximum space remaining between grooves R Rounding radius of the pick-up needle AT Pick-up point SA Safety distance RA (A=O; A=O) Groove spacing with amplitude RA (A+; A-) Groove spacing with diverging amplitudes RA (A; A+) Groove spacing with converging amplitudes SF Sawtooth wall FRB Run-in groove region KRB Indication groove region ARM Run-out groove region MB. Modulation groove region 1 MB, Modulation groove region 2 I claim:

1. A gramophone record comprising a master of recording material in the surface of which are cut grooves which cooperate with a pick-up needle and which have a modulation of frequency corresponding to that of a recorded signal, the grooves being cut into" the original recording material to such a depth that a sharp groove crest is formed from the intersection of the walls of adjacent grooves regardless of the groove spacing and modulation amplitude, the lowest points of said grooves being spaced from a constant flat cutting plane only by an amount proportional to the modulation signal.

2. A record according to claim 1 wherein the groove spacing and the maximum modulation amplitude are preselected so that the minimum groove crest height is a predetermined safe distance above the two pick-up points determined by the size and shape of the pick-up needle to be used.

3. A record according to claim 1 in the surface of which is cut at least one unmodulated guide groove which cooperates with a pick-up needle, wherein in the region of each said guide groove the actual surface thereof is above the entire region of the modulated groove walls.

4. A master disc comprising a disc of recording material in the surface of which are cut grooves which cooperate with a pick-up needle and which have a modulation of frequency corresponding to that of'a recorded signal, the groove being cut into the original recording material to such a depth that a sharp groove crest is formed from the intersection of the walls of adjacent grooves regardless of the groove spacing and modulation amplitude, the lowest points of said grooves being spaced from a constant flat cutting plane only by an amount proportional to the modulation signal.

5. A gramophone record comprising a disc of recording material in the surface of which are cut grooves which cooperate with a pick-up needle and which have a modulation of frequency corresponding to that of a recorded signal, the grooves being cut into the original and recording material to such a depth that a sharp groove crest is formed from the intersection of the walls of adjacent grooves regardless of the groove spacing and modulation amplitude, such groove crests lying a predetermined safe distance below the lowest point of irregularity of the original surface, the crests and bottoms of said grooves being spaced proportionately from a constant flat cutting plane only by an amount proportional to the modulation signal.

6. A method of cutting a groove into the surface of a master of recording material, the method comprising the steps of providing a supporting surface in the form of a turntable mounted for rotation so that its upper surface which supports the master is always in a constant plane, mounting a cutting stylus having a cutting tip above said turntable and said master, with the tip of said stylus being adjusted relative to the constant plane of said turntable so as to provide a flat mean cutting plane for controlling the depth of cut in the master regardless of wobble or surface irregularities in the master, cutting the master by means of said cutting tip at the desired frequency or frequency modulation frequency by positively guiding the cutting stylus with its tip at a depth relative to said mean cutting plane, with such mean cutting plane being located sufficiently below the lowest point of wobble and irregularity of the original surface so that the walls of adjacent grooves intersect and the thus formed groove crests are located substantially below said lowest point of the original surface, with modulation of said grooves varing the depth of said grooves, and thus the location of the groove bottoms and crests, from said mean cutting plane only by an amount proportional to the modulation signal.

7. A method according to claim 6 further comprising cutting a run-in groove, the bottom of the run-in groove being cut at a depth corresponding to said mean cutting plane, and both the groove walls of the run-in groove being cut in a straight line up to the original cutting surface, with a spacing between adjacent run-in groove walls.

8. A method according to claim 6 further comprising cutting a run-out groove, the bottom of the run-out groove being cut at a depth corresponding to said mean cutting plane and both the groove walls of the run-out groove being cut in a straight line up to the original cutting surface, with a spacing between adjacent run-out groove walls.

9. A method according to claim 6 further comprising the cutting of an indication groove between two modulation grooves, the cutting stylus during cutting of the indication groove continuing to cut with its tip at the depth of said mean cutting plane and being advanced with a groove spacing such that both the indication groove wall is cut substantially in the direction of the modulation and the other groove wall is out without modulation at a angle to the perpendicular to the plane of the record, said angle being between 0 and 15. 

1. A gramophone record comprising a master of recording material in the surface of which are cut grooves which cooperate with a pick-up needle and which have a modulation of frequency corresponding to that of a recorded signal, the grooves being cut into the original recording material to such a depth that a sharp groove crest is formed from the intersection of the walls of adjacent grooves regardless of the groove spacing and modulation amplitude, the lowest points of said grooves being spaced from a constant flat cutting plane only by an amount proportional to the modulation signal.
 2. A record according to claim 1 wherein the groove spacing and the maximum modulation amplitude are preselected so that the minimum groove crest height is a predetermined safe distance above the two pick-up points determined by the size and shape of the pick-up needle to be used.
 3. A record according to claim 1 in the surface of which is cut at least one unmodulated guide groove which cooperates with a pick-up needle, wherein in the region of each said guide groove the actual surface thereof is above the entire region of the modulated groove walls.
 4. A master disc comprising a disc of recording material in the surface of which are cut grooves which cooperate with a pick-up needle and which have a modulation of frequency corresponding to that of a recorded signal, the groove being cut into the original recording material to such a depth that a sharp groove crest is formed from the intersection of the walls of adjacent grooves regardless of the groove spacing and modulation amplitude, the lowest points of said grooves being spaced from a constant flat cutting plane only by an amount proportional to the modulation signal.
 5. A gramophone record comprising a disc of recording material in the surface of which are cut grooves which cooperate with a pick-up needle and which have a modulation of frequency corresponding to that of a recorded signal, the grooves being cut into the original and recording material to such a depth that a sharp groove crest is formed from the intersection of the walls of adjacent grooves regardless of the groove spacing and modulation amplitude, such groove crests lying a predetermined safe distance below the lowest point of irregularity of the original surface, the crests and bottoms of Said grooves being spaced proportionately from a constant flat cutting plane only by an amount proportional to the modulation signal.
 6. A method of cutting a groove into the surface of a master of recording material, the method comprising the steps of providing a supporting surface in the form of a turntable mounted for rotation so that its upper surface which supports the master is always in a constant plane, mounting a cutting stylus having a cutting tip above said turntable and said master, with the tip of said stylus being adjusted relative to the constant plane of said turntable so as to provide a flat mean cutting plane for controlling the depth of cut in the master regardless of wobble or surface irregularities in the master, cutting the master by means of said cutting tip at the desired frequency or frequency modulation frequency by positively guiding the cutting stylus with its tip at a depth relative to said mean cutting plane, with such mean cutting plane being located sufficiently below the lowest point of wobble and irregularity of the original surface so that the walls of adjacent grooves intersect and the thus formed groove crests are located substantially below said lowest point of the original surface, with modulation of said grooves varing the depth of said grooves, and thus the location of the groove bottoms and crests, from said mean cutting plane only by an amount proportional to the modulation signal.
 7. A method according to claim 6 further comprising cutting a run-in groove, the bottom of the run-in groove being cut at a depth corresponding to said mean cutting plane, and both the groove walls of the run-in groove being cut in a straight line up to the original cutting surface, with a spacing between adjacent run-in groove walls.
 8. A method according to claim 6 further comprising cutting a run-out groove, the bottom of the run-out groove being cut at a depth corresponding to said mean cutting plane and both the groove walls of the run-out groove being cut in a straight line up to the original cutting surface, with a spacing between adjacent run-out groove walls.
 9. A method according to claim 6 further comprising the cutting of an indication groove between two modulation grooves, the cutting stylus during cutting of the indication groove continuing to cut with its tip at the depth of said mean cutting plane and being advanced with a groove spacing such that both the indication groove walls are cut to extend up to the level of the original cutting surface and with a spacing between the walls of adjacent indication grooves.
 10. A method according to claim 6 for cutting records for perpendicular reproduction, wherein one groove wall is cut substantially in the direction of the modulation and the other groove wall is cut without modulation at a angle to the perpendicular to the plane of the record, said angle being between 0* and 15*. 